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A central aspect of interaction
design is user testing. User testing involves measuring the
performance of typical users doing typical tasks in controlled
laboratorylike conditions. Its goal is to obtain objective
performance data to show how usable a system or product is
in terms of usability goals, such as ease of use or learnability.
More generally, usability testing relies on a combination
of techniques including observation, questionnaires and interviews
as well as user testing, but user testing is of central concern,
and in this chapter we focus upon it. We also examine key
issues in experimental design because user testing has developed
from experimental practice, and although there are important
differences between them there is also commonality.
The last part of the chapter considers how
user behavior can be modeled to predict usability. Here we
examine two modeling approaches (based on psychological theory)
that have been used to predict user performance. Both come
from the wellknown GOMS family of approaches: the GOMS
model and the Keystroke level model. We also discuss Fitts'
The main aims of this chapter are to:
- Explain how to do user testing.
- Discuss how and why a user test differs
from an experiment.
- Discuss the contribution of user
testing to usability testing.
- Discuss how to design simple experiments.
- Describe the GOMS model, the Keystroke
level model and Fitts' law and discuss when these techniques
- Explain how to do a simple keystroke